Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. In the recent past, slide and overhead transparency projectors were commonly used for conducting sales demonstrations, business meetings, and classroom instruction. Slide projectors were commonly controlled by a remote control unit that was electrically connected to the slide projector by a cable that allowed a presenter, such as a salesperson, instructor, or project manager, to stand next to the projector or the projection screen while conducting the slide presentation. However, the cable limited the presenter's mobility and presented a tripping hazard, especially in darkened rooms.
More recently, slide and overhead presentations have been largely replaced by presentations employing multimedia projection systems. In a typical operating mode, multimedia projection systems receive video signals from a personal computer ("PC"), a tape drive, a disk drive, or some other form of image generating or storing device. The video signals may represent still, partial-, or full-motion display images of a type typically rendered by PCs. The video signals are converted in the multimedia projection system into signals that control a digitally driven imaging device that forms the image to be projected.
The presenter typically controls the multimedia projection system with a wireless IR remote control device similar to ones employed to control home television receivers. This has greatly increased the mobility of the presenter and eliminated the tripping hazard. In fact, multimedia projectors have grown in popularity to the point where they are available in diverse models suited for, among others, portable, tabletop, ceiling-hung, and rear-projected applications.
Because battery powered IR remote control devices are typically quite directional, the wide variety of possible projector placements and various possible presenter positions causes a dilemma. The presenter can usually point the IR remote control transmitter toward the multimedia projector, but proper placement of the IR receiver on the multimedia projector is indeterminate. Suitable IR receiver mounting positions may include top mounting when the presenter is standing close to the multimedia projector, front mounting when the presenter is standing near the projection screen, and rear mounting when the presenter is behind the multimedia projector. Top mounting may also be suitable in ceiling-hung applications in which the multimedia projector is hung upside down. Clearly no single IR receiver position was suitable for all applications, so prior workers placed multiple IR receivers on the major surfaces of the multimedia projectors, an unduly complex and costly solution.
Prior IR receivers are directional primarily because the optical components coupling IR energy to an IR sensor have a limited range of angular coverage. Indeed, the most common optical component is merely an optical window having a spectral filtering property that improves the signal-to-noise ratio of the sensed IR energy. Attempts to compensate for the directionality of prior IR receivers included increasing IR transmitter power and/or IR receiver sensitivity. Unfortunately, the former solution unacceptably increased battery consumption and the latter solution was marginal because receiver sensitivity was already typically maximized.
What is needed, therefore, is an IR receiver employing a single IR sensor and having usable sensitivity to received IR energy over a wide range of azimuthal and elevation angles.